Field of the Invention
The present invention relates to measurement system measuring an object by using a captured image acquired through image capturing of the object, and particularly to a projection apparatus projecting a measuring optical image onto the object and to an image capturing apparatus capturing an image of the object.
Description of the Related Art
In the above measurement system, distortion of a projection optical system of the projection apparatus and that of an imaging optical system of the image capturing apparatus deteriorate accuracy of a measurement result of the object. For this reason, correction of a component of the distortion (hereinafter referred to as “a distortion component”) contained in the captured image on a basis of a function expressing the distortion has been conventionally performed.
Japanese Patent Laid-Open No. 07-264577 discloses a method of correcting a distortion component by using a pinhole model in which all light rays entering an imaging optical system pass through one point. Japanese Patent Laid-Open No. 2001-133225 discloses a method that produces, depending on a distance to an object, multiple functions to be used to correct a distortion component and changes the function to be used depending on the distance to the object. Japanese Patent Laid-Open No. 2008-298589 discloses a method of correcting a distortion component by using, not the pinhole model, but an optical system model in which an entrance pupil position of an imaging optical system is changed for respective field angles.
However, since an exit pupil position of the projection optical system and an entrance pupil position of the imaging optical system generally differ for light rays of respective field angles, the distortion components contained in the measuring optical image projected onto the object and in the captured image have different shapes depending on a distance from the object to the optical system. Therefore, the method disclosed in Japanese Patent Laid-Open No. 07-264577 which corrects the distortion component by using the pinhole model cannot perform correction with consideration for the different shapes of the distortion component depending on the distance to the object. As a result, this method cannot sufficiently correct the distortion component over an entire range in a depth direction (that is, an optical axis direction of the optical system) among three-dimensional directions.
The method disclosed in Japanese Patent Laid-Open No. 2001-133225 requires, in order to store the multiple functions provided for the correction of the distortion component depending on the distance to the object, a large memory capacity. Moreover, this method also requires a means to accurately measure the distance to the object, which makes a configuration of the system complicated.
Furthermore, the method disclosed in Japanese Patent Laid-Open No. 2008-298589 which uses the optical system model in which the entrance pupil position is changed for the respective field angles requires a lot of input images to acquire many parameters to be used for producing the model and also requires a complicated calculation process to acquire the parameters.